Volume cycled medical ventilators



United States Patent 3,351,092 VOLUME CYCLED MEDICAL VENTILATOR MauriceErnest Ingerfield, Croydon, and Thomas lil lary Howells, Whetstone,England, assignors to Pye Limited, Cambridge, England Filed Oct. 13,1964, Ser. No. 463,666 Claims priority, application Great Britain, Oct.15, 1963, 40,548/ 63 4 Claims. (Cl. 137624.14)

ABSTRACT OF THE DISCLOSURE A volume cycled medical ventilator includes abellows for supplying gas to a patient during an inhalation periodthrough a changeover valve in a first position and a valve controllingmechanism for moving the valve to a second position to allow the patientto exhale to atmosphere in an exhalation period. The valve controllingmechanism is movable by a lever connected to the bellows to eitect achange between the inhalation and exhalation periods when the volume ofgas in the bellows reaches maximum or minimum limits. The valvecontrolling mechanism includes magnetic means for holding the valve inthe first or second positions against the bias of springs until thechange in volume of the bellows increases the spring pressure enough toovercome the magnetic means. Consult the specification for furtherdetails and features of the invention.

This invention relates to medical ventilators used to supply air, oxygenor anaesthetic gases to a patient in the application of artificialrespiration or for apnoeic states in anaesthesia.

Modern ventilators control the supply of gas to the patient duringinspiration periods, and permit or encourage the emptying of thepatients lungs during an ensuing expiration period. It is customary toprovide means for controlling the rhythm of the machine, and this may bedetermined by sensing the volume or pressure of the gas, or by timingthe duration of the two periods in each cycle. When used with a gassupply giving a constant rate offlow, the time, pressure and volume arerelated, but the ventilator is said to be time-cycled if it normallysupplies gas for a pre-determined period; pressure-cycled if it suppliesgas until a pre-determined pressure is achieved, and volume-cycled if itmeasures a pre-determined volume of gas to be delivered to the patientin each cycle. The motive energy for the cycling means may be derivedfrom an external source, such as an electrical power supply, anadditional supply of gas under pres sure, or they may be activatedentirely by the gas supply for the patient, either by permitting acertain wastage of gas to operate a change-over mechanism, or by storingenergy during one period by compressing a spring, for example, andutilising the stored energy to motivate the second period of each cycle,to give a completely self-energised machine.

The advantage of simplicity and portability has led to several proposalsfor self-energised volume-cycled ventilators, in which gas is fed to abellows during an expiration period whilst the gas is emptying from thepatients lungs via an outlet valve to atmosphere, and upon the bellowsexpanding to a pre-determined size, a changeover mechanism is acted uponby the bellows to close the outlet valve and open an inlet valve topermit gas from the bellows to be fed to the patient, the bellows beingurged to contract by a spring or the like. Upon the bellows contractingto a second pre-determined size the change-over mechanism is againoperated by the bellows, to terminate the inspiration period andcommence a new cycle. Attempts to provide volume-cycled venti:

3,351,992 Patented Nov. 7, 1967 lators of this type have taken variousforms, but no machine has met with universal acceptance, because it hasproved difiicult to supply a change-over mechanism capable of simpleoperation yet giving adequate sensitivity and accuracy, and furthermore,in some conditions met with in normal practice, these machines have beenknown to stall, that is to say, the rhythmic cycling has ceased.

One object of the present invention is to provide a selfenergisedvolume-cycled ventilator that is simple to operate, yet at the same timeaccurate and reliable in use.

The present invention is a volume cycled medical ventilator including abeilows to which gas is fed during the expiration period when gasalready in the lungs of a patient is being exhausted therefrom, and achange over mechanism operated upon the bellows expanding by apre-determined amount due to the gas flowing into the bellows, theoperation of said change over mechanism opening a valve to initiate theinspiration period and allow the gas in the bellows to flow out of thebellows during the inspiration period under the action of spring meansor the like acting on the bellows until the bellows is contracted to aposition at which the change over mechanism is again operated to closethe valve in the outlet from the bellows and allow the next expirationperiod to commence, during which the gas fed to the bellows againexpands the bellows.

One feature of the present invention is a self energised volume-cycledmedical ventilator employing a valve for the control of gas flow from abellows, in which spring means or the like are adapted to urge saidvalve towards the closed position and a magnetic circuit including aportion movable with said valve is provided to hold said valve in theopen position against the pressure of said spring means when the air gapin said magnetic circuit is less than a pre-determined size, and meansassociated with the expansion and contraction of the bellows of saidventilator, mechanically to move said valve and movable portion to aposition at which the air gap exceeds said pro-determined size whereuponsaid spring urges said valve to the closed position.

According to a further feature of the present invention a self-energisedvolume-cycled medical ventilator employs a change-over mechanism for thecontrol of gas flow between a bellows of said ventilator and a patient,and between the patient and an outlet to atmosphere, an inlet valve andan outlet valve linked to move together in which said inlet is held inthe open position by a magnetic circuit until an air-gap, introducedinto said magnetic circuit by the contraction of the bellows of saidventilator, exceeds a predetermined size, whereupon spring means or thelike urge said inlet valve closed and said outlet valve open, saidoutlet valve then being held open by a further magnetic circuit until anair gap is introduced in said further circuit by the expansion of saidbellows.

According to yet another feature of the present invention, a bellowsoperated volume-cycled ventilator employs a pressure relief valveconnected in the gas circuit at a point between the inlet valve and theoutlet valve, and controlling a further outlet to atmosphere, saidrelief valve being urged to the closed position by spring means, or thelike, and a magnetic circuit associated with said valve and including aportion moving with said valve, said magnetic circuit being adapted tohold said valve open when the air gap in said magnetic circuit isreduced below a pre-determined size by the rise of pressure in said gascircuit, and means associated with the contraction of the bellows ofsaid ventilator to introduce an air gap in said magnetic circuit greaterthan said predetermined size, whereupon said spring means urge saidrelief valve to the closed position.

In an arrangement such as the above a gas operated resonator isconnected in the gas circuit controlled by the pressure relief valvesuch that the resonator is exited by the passage of gas to atmospherethrough the pressure relief valve giving audible warning of the pressurerelief being in the open position.

The above and other features of the invention will be more readilyunderstood by a perusal of the following description having reference tothe accompanying drawing which is a diagrammatic representation of aventilator in accordance with the present invention.

The apparatus comprises a bellows 1 to which gas is fed from a supplyattached to an input port 2. The gas gas supply may include means forproviding a constant flow of gas, and the input to the bellows may becontrolled by a valve adapted to prevent over-expansion of the bellows.

The bellows is connected to a lever in the form of a movable plate 3,which is hinged to rotate at pivot 4, so that as the bellows is expandedby the incoming gas the plate 3 is rotated in an anti-clockwisedirection about the pivot 4, and as volume in the bellows falls theplate is rotated in a clock-wise direction due to the weight of theplate 3. An outlet 5 from the bellows, which leads to a valve assembly6, and all of the subsequent gas circuit with the exception of avariable constriction (hereinafter described), is of a sufficientlylarge diameter to allow for a high instantaneous rate of gas flow. Thevalve assembly 6 comprises two valves, 6A and 6B coupled by a rod 6D.The inlet valve 6A is shown in the closed position, and the outlet valve6B is shown open, the valves being separated by a gas tight seal 6C. Inthe position shown, incoming gas from the supply 2 has caused thebellows to expand, and a patient using the machine is free to breath outvia a connection 7 and an outlet 8 to atmosphere. As will be explainedlater, expansion of the bellows to a pre-determined volume causes achangeover mechanism 9 to move the valve assembly 6 to an alternativeposition, in which the valve 63 prevents gas passing from the patientslungs to atmosphere, and valve 6A opens to permit gas from the bellowsto pass via the variable constriction 10 and a connection 11 to thepatient. For any given volume of gas, the duration of the expirationperiod is determined by the rate of flow from the gas supply, and theduration of the inspiration period is determined by the setting of thevariable constriction 18. To prevent the machine from stalling incertain adverse clinical conditions, a pressure-relief valve 12 isconnected to the connection 11. A valve-plunger 13 prevents the escapeof gas to atmosphere via outlet 14 during normal working, but as thepressure of gas in connection 11 rises the plunger 13 and its associatedmagnetic member 15 is forced to move against a spring 16 towards amagnet 17, and at a pre-determined pressure level the plunger will reacha position in which the air-gap in the magnetic circuit is small enoughto permit the magnet 17 to overcome the spring 16 and so pull theplunger 13 to the open position and hold it there. A reduction in volumeof the bellows as gas passes to atmosphere via outlet 14 causes theplate 3 to descend, and at the end of the inspiration period a pin 18attached to the plate strikes a member 19 attached to the plunger 13,causing the magnetic member to move away from the magnet 17. Spring 16closes the valve thus blocking outlet 14. The magnet 17 is adjustablymounted in the valve 12, and the point of engagement of members 18 and19 may be adjusted to give precise operation.

The connection of a whistle (not shown) to outlet 14 will, when plunger13 is held by magnet 17, allow gas to flow through the whistle to escapeto atmosphere and during the passage of such gas through the whistle anaudible signal will be given to warn the operator of the opened pressurerelief valve.

The mechanism 9 for changing the position of valve assembly 6 utilizes alever 20, pivotally mounted at 21 and linked to the valve rod 6D at 22.Attached to the lever 20 are two magnetic members 23, 24. Two permanentmagnets 25, 26 are mounted on the supporting framework to contact themembers 23, 24. In the expiration position, as shown, member 23 is heldby magnet 25, so holding the inlet valve 6A closed, the power of themagnet being sufficient to overcome the pressure of a spring 27 on a rod28 slidably mounted in the lever 20. The expanding bellows moves theplate 3 until a rod 29 on the plate 3 acts via a wedge 30 upon the rod28 with sufiicient force to compress spring 27 and to move the magneticmember 23 away from the magnet 25, whereupon the spring 27 forces thelever 20 to rotate until magnetic member 24 engages with magnet 26 whichholds the lever in position with outlet valve 63 closed to institute aninspiration period. Means may be provided to adjust the position ofmagnets 25, 26, on the supporting framework (not shown).

The inspiration period is terminated when contraction of the-bellows 1has permitted the plate 3 to move to a position in which a rod 31slidably mounted in the lever 20 is engaged by a disc 32, fixed on theplate 3, with sufficient force to compress a spring 33 and to move themagnetic member 24 away from the magnet 26, whereupon the spring 33 willmove the lever 9 back to the expiration position.

Control of the volume of gas delivered in each cycle is provided byadjustment of the wedge 30, having a pivot 34 adjustably positioned onthe supporting framework (not shown). Movement of the pivot 34 towards apoint 35 will reduce the volume of gas delivered as the movement ofplate 3 required to engage pin 29 will be reduced, whilst movement ofthe pivot 34 in the other direction, towards a point 36 will increasevolume of gas delivered. This adjusting movement may be provided in anumber of Ways, e.g. by a chain passing over a rotary control shaft.This would permit the control to be obtained by rotation of aconventional pointer knob on the front panel of the machine, and hasbeen found to be more desirable than a slide adjustment. The wedge 30can also be used to provide for setting the machine to function with amanual control bag, as is often required in anaesthesia, by arrangingthat in the extreme position, in the region of point 35, the wedge 30applies holding pressure upon rod 28, so that no movement of the plate 3occurs and the inlet valve 6A remains open.

The ventilator described may be used with closed'circuit breathingtechniques, and negative pressure can be obtained by attaching suctionmeans to outlet 8 to provide a negative phase. One-way valves, andsafety valves may be fitted, and auxiliary items may be incorporated,for example a pressure gauge may be connected to the connection 11, anda volumeter may be attached at outlet 8.

Choice of the spring pressures and magnets, provides a precise andreliable operation, and facilitates the production of machines havingconstant and readily controllable characteristics. Various modificationscan be made without departing from the scope of the invention, forexample a single magnetic member could be used in place of the twomembers 23, 24. Furthermore a permanent magnet could be made to movewith respect to a stationary magnetic member, or both the moving andstationary portions of a magnetic circuit could be formed by permanentmagnets.

We claim:

1. A volume cycled respirator comprising a bellows 0peratively connectedwith a lever, an inlet port connecting the interior of the bellows witha continuous pressure gas supply, an outlet duct for said bellowscommunicating with a valve chamber, in said chamber a valve which in afirst position blocks an outlet duct from a patient while permitting thepassage of pressure gas through the chamber to an inlet duct to thepatient, whereas in a second and alternative position said valve ermitsthe said outlet duct to have free access to atmosphere while blockingthe passage of gas through the chamber to the inlet duct, a valvecontrolling mechanism which at the end of the inspiratory period isoperated by said lever to move the said valve from said first positionto said second position and comprising means which, on the volume of gasin said bellows having reached a predetermined upper magnitude, causesaid lever to operate the valve control mechanism to return the valve tothe first said position and comprising spring means adapted to urge saidvalve towards the second position and a magnetic circuit including aportion movable with said valve and adapted to hold said valve in thefirst position against the pressure of said spring means when the springpressure is less than a predetermined magnitude, and means associatedwith the contraction of the bellows of said ventilator, mechanically toincrease said spring pressure to a magnitude greater than saidpredetermined magnitude whereupon said spring breaks the magneticcircuit and urges said valve to the second position.

2. A volume cycled respirator as claimed in claim 1 further comprising asecond spring means for urging the valve toward the first position and asecond magnetic circuit including a portion movable with said valve andadapted to hold said valve in the second position against the pressureof said second spring means when the second spring pressure is less thana predetermined magnitude and means associated with the expansion ofsaid bellows mechanically to increase said second spring pressure to amagnitude greater than said predetermined magnitude whereupon saidsecond spring breaks the second magnetic circuit and urges the valve tothe first position.

3. A volume cycled respirator as claimed in claim 2 further comprising apressure relief valve connected to the inlet duct to the patient, andcontrolling a further outlet to atmosphere, said relief valve beingurged to the closed position by third spring means, and a third magneticcircuit associated with the pressure relief valve and including aportion movable with the relief valve, said third magnetic circuit beingadapted to hold said relief valve open when the air gap in the thirdmagnetic circuit is reduced below a predetermined size by the rise ofpressure in said inlet duct, and means associated with the contractionof the bellows to introduce an air gap in said third magnetic circuitgreater than said predetermined size, whereupon said third spring meansurge said relief valve to the closed position.

4. A volume cycled respirator as claimed in claim 2 in which the saidmeans associated with the expansion of the bellows to increase thesecond spring pressure includes abutment means between said lever andsaid second spring means adapted to compress the second spring meanswhen the bellows is expanded, said. abutment means including a wedgemember movable to adjust the expansion of the bellows necessary to causethe second spring means to move the valve to the first position.

References Cited UNITED STATES PATENTS 1,044,031 11/1912 Drager 128-292,071,215 2/ 1937 Petersen 137624. 14 X 2,273,790 2/1942 Raymond 128-292,575,086 11/1951 Atchison 251 2,870,763 1/1959 Stanton 128--29 FOREIGNPATENTS 250,763 10/ 1962 Australia.

WILLIAM F. ODEA, Primary Examiner. R. GERARD, Assistant Examiner.

1. A VOLUME CYCLED RESPIRATOR COMPRISING A BELLOWS OPERATIVELY CONNECTEDWITH A LEVER, AN INLET PORT CONNECTING THE INTERIOR OF THE BELLOWS WITHA CONTINUOUS PRESSURE GAS SUPPLY, AN OUTLET DUCT FOR SAID BELLOWSCOMMUNICATING WITH A VALVE CHAMBER, IN SAID CHAMBER A VALVE WHICH IN AFIRST POSITION BLOCKS AN OUTLET DUCT FROM A PATIENT WHILE PERMITTING THEPASSAGE OF PRESSURE GAS THROUGH THE CHAMBER TO AN INLET DUCT TO THEPATIENT, WHEREAS IN A SECOND AND ALTERNATIVE POSITION SAID VALVE PERMITSTHE SAID OUTLET DUCT TO HAVE FREE ACCESS TO ATMOSPHERE WHILE BLOCKINGTHE PASSAGE OF GAS THROUGH THE CHAMBER TO THE INLET DUCT, A VALVECONTROLLING MECHANISM WHICH AT THE END OF THE INSPIRATORY PERIOD ISOPERATED BY SAID LEVER TO MOVE THE SAID VALVE FROM SAID FIRST POSITIONTO SAID SECOND POSITION AND COMPRISING MEANS WHICH, ON THE VOLUME OF GASIN SAID BELLOWS HAVING REACHED A PREDETERMINED UPPER MAGNITUDE, CAUSESAID LEVER TO OPERATE THE VALVE CONTROL MECHANISM TO RETURN THE VALVE TOTHE FIRST SAID POSITION AND COMPRISING SPRING MEANS ADAPTED TO URGE SAIDVALVE TOWARDS THE SECOND POSITION AND A MAGNETIC CIRCUIT INCLUDING APORTION MOVABLE WITH SAID VALVE AND ADAPTED TO HOLD SAID VALVE IN THEFIRST POSITION AGAINST THE PRESSURE OF SAID SPRING MEANS WHEN THE SPRINGPRESSURE IS LESS THAN A PREDETERMINED MAGNITUDE, AND MEANS ASSOCIATEDWITH THE CONTRACTION OF THE BELLOWS OF SAID VENTILATOR, MECHANICALLY TOINCREASE SAID SPRING PRESSURE TO A MAGNITUDE GREATER THAN SAIDPREDETERMINED MAGNITUDE WHEREUPON SAID SPRING BREAKS THE MAGNETICCIRCUIT AND URGES SAID VALVE TO THE SECOND POSITION.